In PTL 1, it is described that “Included are first control means 1B including detecting means 108 for detecting a voltage variation of a system, constant time occurrence checking means 109 for detecting and storing whether or not the voltage variation periodically occurs at a constant time, and state evaluating means 110 for predicting the system voltage after variation from the system voltage detected before a predetermined time of the occurrence time and selecting a tap of a voltage regulator that absorbs the variation, second control means 1C for changing the tap of the voltage regulator by an integral value of the deviation from the system voltage, and logic processing means for prioritizing anyone of the first control means 1B and the second control means 1C”.